Re: [PATCH v4 30/31] mm: memcontrol: eliminate the problem of dying memory cgroup for LRU folios

[Usama Arif]

> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index e7d4e4ff411b6..0e0efaa511d3d 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -247,11 +247,25 @@ static inline void reparent_state_local(struct mem_cgroup *memcg, struct mem_cgr
>  
>  static inline void reparent_locks(struct mem_cgroup *memcg, struct mem_cgroup *parent)
>  {
> +	int nid, nest = 0;
> +
>  	spin_lock_irq(&objcg_lock);
> +	for_each_node(nid) {
> +		spin_lock_nested(&mem_cgroup_lruvec(memcg,
> +				 NODE_DATA(nid))->lru_lock, nest++);
> +		spin_lock_nested(&mem_cgroup_lruvec(parent,
> +				 NODE_DATA(nid))->lru_lock, nest++);
> +	}
>  }
>  

mWould this break lockdep on more than 4 NUMA nodes as MAX_LOCKDEP_SUBCLASSES = 8 and
2 locks are being acquired per node.

>  static inline void reparent_unlocks(struct mem_cgroup *memcg, struct mem_cgroup *parent)
>  {
> +	int nid;
> +
> +	for_each_node(nid) {
> +		spin_unlock(&mem_cgroup_lruvec(parent, NODE_DATA(nid))->lru_lock);
> +		spin_unlock(&mem_cgroup_lruvec(memcg, NODE_DATA(nid))->lru_lock);
> +	}
>  	spin_unlock_irq(&objcg_lock);
>  }